It is permanently haram for a Muslim to marry a woman who belongs to one of the following categories:

The father’s wife, whether divorced or widowed. During the period of jahiliyyah such marriages were allowed. Then Islam prohibited them, for once a woman is married to a man’s father she acquires the status of his mother, and this prohibition is out of honor and respect for the father. Moreover, as this inviolable prohibition leaves no room for sexual attraction between the son and his step-mother, they are able to develop a relationship of respect and honor.

The mother, including the grandmothers on both sides.

The daughter, including the granddaughters from the son or daughter.

The sister, including the half, and step-sisters.

The paternal aunt, whether she is the real, half, or step-sister of the father.

The maternal aunt, whether she is the real, half, or step-sister of the father.

The brother’s daughter, i.e., his niece.

The sister’s daughter, i.e., her niece.

All these female blood-relatives are a man’s muharramat and he is mahrem to his corresponding female relatives. Marriage to any mahrem whomsoever is permanently prohibited. The reasons for this prohibition are as follows.

Entertaining any sexual thoughts concerning such close relatives as one’s mother, sister, and daughter is instinctively abhorrent to human nature; there are even certain animals which avoid mating with such closely-related animals. The respect a man feels for his aunts is like the respect he has for his mother, and likewise uncles are regarded as fathers.

Since the family must live together in intimacy and privacy but without incestuous relations, the Shari’ah intends to cut at the roots of any sexual attraction among such close relatives.

Since there is natural love and affection among such close blood relatives, the intent of the Shari’ah is to expand the circle of love and kinship by prohibiting incest and thereby directing the man’s search for women outside the family. Thus each marriage extends the sphere of love, bringing new people within this ever-expanding network of affection: “And He has put love and mercy between you.” (Surah 30: Verse 21)

The natural sentiments of love and affection between a man and the above-mentioned female relatives must be kept strong forever. If marriage were permitted between such relatives, it would cause jealousies, dissensions, and the disruption of families, destroying the very sentiments of love and affection which give cohesiveness and permanence to the family structure.

The offspring of marriages to such close blood relatives would most probably be defective and weak. Moreover, if physical or mental defects are present in the members of a family, they would become more pronounced among the children of such marriages.

The woman needs someone to champion her rights and support her case against her husband, especially when relations between the two of them become strained. If those women who could defend her became rivals, how would this be possible?

Marriages Prohibited by Reason of Fosterage

The foster mother: It is haram for a Muslim to marry a woman who has suckled him during his infancy, for suckling makes her like his real mother, since milk has gone into the making of his flesh and bones. Nursing consciously or unconsciously produces feelings of motherhood in a woman and of kinship in a child, and although these feelings might seem to disappear as the child grows and becomes a man, they remain hidden in the unconscious.

However, the prohibition of marriage based on fosterage is effective only if the suckling occurred before the time of weaning; that is, when milk was the primary source of food. Another condition is that the child has suckled his fill on five separate occasions, a fill being defined as when the child leaves off suckling of his own accord. After a survey of all the ahadith on this subject, the fixing of five sucklings as the minimum seems to be the preferred view.

Foster sisters: Just as a woman become a mother to a child by virtue of suckling, likewise her daughters become his sisters, her sisters his aunts, and so on. The Prophet (peace be on him) said: “What is haram by reason of genealogy is haram by reason of fosterage.” (Reported by al-Bukhari and Muslim.) Thus the foster-sisters, foster-aunts, and foster-nieces are all muharramat and marriage to them is permanently prohibited.

In-law Relationships

The mother-in-law: Marriage to the wife’s mother is permanently prohibited from the time a man enters into a marriage contract with a woman, whether he and his wife have engaged in sexual intercourse or not. The act of marriage itself gives the mother-in-law the same status as the mother.

The step-daughter: A man cannot marry his step-daughter (his wife’s daughter by a previous marriage) if sexual intercourse has taken place with her mother, his wife. However, if a man divorces his wife without having had intercourse with her, it is permissible for him to marry her daughter by a previous marriage.

The daughter-in-law: That is, the wife of the real son, not that of the adopted son. In fact, Islam abolished the permissibility of the system of legal, formalized adoption, because this is contrary to fact and to reality, resulting in the prohibiting of what is essentially halal and the permitting of what is essentially haram. Allah Ta’ala says: ...Nor has He made your sons by adoption your (real) sons. Those are simply words from your mouths....(33:4) meaning that it is merely an expression of the language which does not alter reality nor transform an outsider to the family into a blood relative.

These three types of female relatives are forbidden in marriage in order that peaceful relationships may be maintained among the in laws.

Sisters as Co-Wives

As opposed to the practice of the period of jahiliyyah (pre-Islamic era), Islam forbade taking two sisters as co-wives at the same time, because the feeling of love and sisterliness which Islam wants to maintain between sisters would be destroyed if one sister became the co-wife of the same husband.

While the Qur’an mentioned the two sisters, the Prophet (peace be on him) added, “A man may not be married to a woman and her paternal aunt (at the same time), nor to a woman and her maternal aunt”. (Reported by al-Bukhari and Muslim.) and he said, “If you do this, you will sever your ties of kinship.” (Reported by Ibn Hibban.) And how could Islam permit the breaking of such kinship ties when it places so much importance on them?

Married Women

As long as a woman is married, her marriage to any other man is prohibited. She may marry another man only when two conditions are fulfilled:

Her marriage tie is broken either because of the death of her husband or because of divorce;

She has completed the period of waiting (‘iddah) ordained by Allah. For a pregnant woman this period ends when she delivers the baby. If she is widowed but not pregnant, the period of ‘iddah is four months and ten days, while if she is divorced and it is not known whether or not she is pregnant, the ‘iddah is three menstrual cycles. This ‘iddah relates to the woman who has menstrual periods; for a woman who does not menstruate, the ‘iddah is three months.

Allah Ta’ala says:

“And divorced women shall wait concerning themselves for three monthly periods. And it is not permissible for them to conceal what Allah has created in their wombs, if they believe in Allah and the Last Day.” (Surah 2: Verse 228)

“...and As for those who have no further expectation of menstruation among your women, if you are in doubt, the waiting period is three months, as well as for those who have no menses. And for those who are pregnant, their period is until they deliver their burdens.” (Surah 65: Verse 4)

And, “For those of you who die and leave behind widows, they shall wait concerning themselves for four months and ten days...” (Surah 2: Verse 234).

Of these fifteen categories of female relatives to whom marriage is prohibited, fourteen are mentioned in Surah al-Nisa:

“And do not marry those women whom your fathers married, except what is past; indeed, it was an indecency and an abomination, and an evil path. Forbidden to you are your mothers and your daughters, and your sisters and your father’s sisters and your mother’s sisters, and your brothers’ daughters and your sisters’ daughters, and your foster mothers and your foster sisters, your wives’ mothers, your stepdaughters under your guardianship born of your wives to whom you have gone in—and if you have not gone into them there is no blame on you—and the wives of your sons proceeding from your loins, and that you should marry two sisters at one time, except what is past; indeed Allah is Forgiving, Merciful.” (Surah 4: Verses 22-23)

The prohibition against being married to a woman and any of her aunts at the same time is derived from the hadith cited above.